CHAPTER XIII. 



EFFECT OF HEAT AND VOLATILE ANTISEPTICS ON 



SOIL BACTERIA. 



SOILS are often heated, steamed, or treated with volatile or non- 

 volatile antiseptics both for experimental and practical purposes. 

 The process is not sufficient to destroy all forms of life within the soil. 

 It only destroys some of the weaker species and the aim is usually to 

 destroy an injurious species. Yet the process is often referred to 

 as sterilization. In view of the fact that they fail to render the soil 

 sterile, some workers prefer the terms partial sterilization or pas- 

 teurization, which more accurately describe the process. 



Although it was well known that the kiln-burning of clay produced 

 a far-reaching chemical and physical effect, yet soil investigators 

 considered that the process of sterilization produced no change 

 either in the mechanical nature or chemical composition of a soil 

 until the work of Frank appeared in 1888. He found that heated 

 soils contained a great deal more soluble matter than unheated soil, 

 peaty soils containing more than twice as much and heated sandy 

 soils not quite twice as much. This increased soluble matter he 

 considered sufficient to account for the increase in crops which was 

 often found to follow the heating of a soil. 



A great impetus was given to the work in 1894 by Oberlin in 

 Germany and Girard in France who found that the application of 

 carbon bisulphid increased the crop-producing power of the soil. 

 Oberlin found that vineyards treated with carbon bisulphid to kill 

 phylloxera showed greatly increased productivity after the treat- 

 ment, and he founded on this his system of grape culture, where 

 fallowing and rotation could be dispensed with in the resetting of 

 vineyards. Girard noticed that soil treated with carbon bisulphid 

 for the purpose of combating a parasitic disease of sugar-beet was 

 more productive than it was before such treatment. The beneficial 

 influence of the treatment extended even into the second year. 

 These facts stimulated investigation and created much discussion, 

 particularly as to the manner of its action. No working hypothesis 

 was, however, formulated until 1899 when Koch announced his 

 direct "stimulation theory," since which time numerous theories 

 have been formulated to account for the noted phenomena. 



Influence on Plant. The use of carbon bisulphid at the rate of 2904 

 pounds an acre resulted in a gain of 15 to 46 per cent, in the yield 



